Warming is causing significant changes to catchment hydrology and vegetation characteristics in the Arctic, which may alter riverine nitrogen (N) export to N-limited coastal ecosystems. To better understand the trajectory of change, along with the underlying mechanisms, there is a need to quantify the seasonality of N export over the entire flowing-water season, encompassing the spring thaw period, through peak summer, to the fall senescent period just before refreezing. Here, we use a 20-year dataset of river chemistry and streamflow, combined with remotely-sensed snow and vegetation cover for the Zackenberg River Basin (NE Greenland), to quantify seasonal and decadal changes in riverine N loss. On average, the duration of the flowing-water season has increased by 40 days from 2003 to 2022, resulting in a seasonal expansion of the shoulder periods (i.e., thaw period and senescence). In general, dissolved inorganic N (DIN) export during the thaw period increased, while the sum total of dissolved organic N (DON) export decreased over the 20yr period. As such, DIN is becoming an increasingly significant portion of TDN export, with a clear shift between early and late decades. Bayesian Model Averaging suggested that nitrate-N export was influenced by the period onset date and period duration, especially during the shoulder periods. In contrast, interannual variability in total ammonium-N and DON export was influenced by variation in global- and regional-scale weather metrics [e.g., multi-variate ENSO index (MEI); Greenland Blocking Index (GBI)]. Overall, we highlight the complexity of fluvial N cycling in the Arctic under a changing climate, the combined role of melting and vegetation dynamics, and the potential for distinct drivers of N export across seasonal periods and among N solutes.